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Abstract:

The present inventions provide a capacitive transducer that can reduce
film damage on a substrate surface on a vibration film side due to a
difference in thermal expansion coefficient between a through wiring and
a substrate and a method of manufacturing the same. The capacitive
transducer consists of a plurality of cells with each cell comprising a
first electrode and a vibration film on a first surface side of a
substrate having a through wiring that penetrates the substrate from a
first surface to a second surface of the substrate, the vibration film
including a second electrode that is formed with a gap from the first
electrode. A holding member that holds a leading end of the through
wiring is provided on the first surface side of the substrate.

Claims:

1. A method of manufacturing a capacitive transducer consists of a
plurality of cells with each cell comprising a first electrode and a
vibration film on a first surface side of a substrate having a through
wiring that penetrates the substrate from a first surface to a second
surface of the substrate, the vibration film including a second electrode
that is formed with a gap from the first electrode, the method
comprising: forming a holding member that holds a leading end of the
through wiring, on the first surface side of the substrate having the
through wiring; and forming the cell after the forming of the holding
member.

2. The method of manufacturing the capacitive transducer according to
claim 1, wherein the forming of the holding member includes forming the
holding member such that the holding member has an opening for exposing
part of the leading end of the through wiring.

3. The method of manufacturing the capacitive transducer according to
claim 1, wherein the forming of the cell comprises: forming the first
electrode on the first surface side of the substrate; forming a sacrifice
layer on the first electrode; forming the second electrode on the
sacrifice layer; and etching the sacrifice layer.

4. The method of manufacturing the capacitive transducer according to
claim 3, wherein the forming of the first electrode is such that the
first electrode is electrically connected to the through wiring.

5. The method of manufacturing the capacitive transducer according to
claim 3, wherein the forming of the second electrode is such that the
second electrode is electrically connected to the through wiring.

6. A capacitive transducer consists of a plurality of cells with each
cell comprising a first electrode and a vibration film on a first surface
side of a substrate having a through wiring that penetrates the substrate
from a first surface to a second surface of the substrate, the vibration
film including a second electrode that is formed with a gap from the
first electrode, wherein a holding member that holds a leading end of the
through wiring is provided on the first surface side of the substrate.

7. The capacitive transducer according to claim 6, wherein a yield stress
of the holding member in a length direction of the through wiring is
equal to or more than 1.7 times a shear strength of the through wiring.

8. The capacitive transducer according to claim 6, wherein the holding
member has a thermal expansion coefficient closer to the thermal
expansion coefficient of the substrate than the thermal expansion
coefficient of the through wiring.

9. The capacitive transducer according to claim 6, wherein the holding
member is made of a silicon compound, and the through wiring is made of a
material containing metal.

10. The capacitive transducer according to claim 6, wherein part of the
leading end of the through wiring and the first electrode are connected
to each other in an opening of the holding member.

11. The capacitive transducer according to claim 6, wherein part of the
leading end of the through wiring and the second electrode are connected
to each other in an opening of the holding member.

12. A subject information acquiring apparatus comprising: the capacitive
transducer according to claim 6; and a processing unit that acquires
information of a subject using an electric signal received from the
transducer, wherein the transducer receives an acoustic wave from the
subject, and converts the acoustic wave into the electric signal.

13. The subject information acquiring apparatus according to claim 12,
further comprising a light source, wherein the transducer receives a
photoacoustic wave generated by irradiating the subject with light
emitted from the light source, and converts the received wave into an
electric signal, and the processing unit acquires the information of the
subject using the electric signal.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a capacitive transducer used as an
ultrasonic conversion element and a method of manufacturing the
capacitive transducer.

[0003] 2. Description of the Related Art

[0004] Up to now, a capacitive transducer (capacitive micromachined
ultrasonic transducer (CMUT)) manufactured using micromachining
technology has been studied as an alternative to a piezoelectric element.
The CMUT can transmit and receive acoustic waves by means of vibrations
of a vibration film, and can be easily provided with excellent broadband
characteristics particularly in liquid. Note that, herein, the acoustic
waves include waves called sonic waves, ultrasonic waves and
photoacoustic waves. For example, the acoustic waves include
photoacoustic waves that are generated inside of a subject by irradiating
the inside of the subject with light (electromagnetic waves) such as
visible light and infrared light. In actual use, a plurality of vibration
films placed in a two-dimensional array is defined as one element, and a
plurality of the elements is further arranged on a substrate, whereby a
transducer is configured so as to achieve desired performance. In order
to independently control each element, wiring electrodes respectively
corresponding to the elements need to be formed. In this case, in order
to reduce a structure size and the parasitic capacitance of each wiring
electrode, it is desirable to use a through wiring that passes through
the substrate. Meanwhile, in the case where the material of the through
wiring is different from the material of the substrate, an end part of
the through wiring may protrude from the substrate surface to deform or
break through thin films located above the end part of the through
wiring, due to a difference in thermal expansion coefficient in a
high-temperature process after the formation of the through wiring.

[0005] U.S. Pat. No. 6836020 discloses a CMUT including a substrate made
of silicon and a through wiring made of polycrystalline silicon. In this
configuration, the through wiring made of polycrystalline silicon and the
substrate made of silicon have approximately similar thermal expansion
coefficient as each other, and hence a change in position of an end part
of the through wiring relative to the substrate surface is small even at
high temperature. Moreover, Japanese Patent Application Laid-Open No.
2007-215177 discloses a CMUT in which a glass substrate having a through
wiring formed therein and another substrate are joined to each other. In
this configuration, when thin films including a vibration film are formed
on the other substrate, the thin films are not influenced by the through
wiring. Moreover, Japanese Patent Application Laid-Open No. 2012-99518
discloses a through wiring structure configured using a concave part and
a plurality of fine holes formed on the bottom surface of the concave
part. In this two-stage wiring configuration, because the fine holes are
small, a stress applied to thin films located above an end part of the
through wiring is small even at high temperature.

[0006] However, in the case of the through wiring made of polycrystalline
silicon in U.S. Pat. No. 6836020, because the resistivity of the
polycrystalline silicon is high, it is far from easy to reduce the
resistance of the through wiring. In the case of the joining method in
Japanese Patent Application Laid-Open No. 2007-215177, a lower electrode
is directly connected to an end part of the through wiring, and hence
deformation of the lower electrode due to thermal deformation of the
through wiring is unavoidable. Furthermore, in the case of the two-stage
wiring configuration in Japanese Patent Application Laid-Open No.
2012-99518, the number of manufacturing steps is large, and a substrate
area occupied by the through wiring is large. Hence, this configuration
is not suitable for a reduction in size.

SUMMARY OF THE INVENTION

[0007] In view of the above-mentioned problems, the present invention
provides a method of manufacturing a capacitive transducer having a cell
comprising a first electrode and a vibration film on a first surface side
of a substrate having a through wiring that passes through the substrate
between a first surface and a second surface of the substrate, the
vibration film including a second electrode that is formed with a gap
from the first electrode. The method comprises: forming a holding member
that holds a leading end of the through wiring, on the first surface side
of the substrate having the through wiring; and forming the cell after
forming the holding member.

[0008] Moreover, in view of the above-mentioned problems, the present
invention provides a capacitive transducer having a cell comprising a
first electrode and a vibration film on a first surface side of a
substrate having a through wiring that passes through the substrate
between a first surface and a second surface of the substrate, the
vibration film including a second electrode that is formed with a gap
from the first electrode. A holding member that holds a leading end of
the through wiring is provided on the first surface side of the
substrate.

[0009] Further features of the present invention will become apparent from
the following description of exemplary embodiments with reference to the
attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1A and FIG. 1B are diagrams for describing an example
capacitive transducer according to the present invention.

[0012] FIG. 3A and FIG. 3B are diagrams for describing an example
information acquiring apparatus including the capacitive transducer
according to the present invention.

DESCRIPTION OF THE EMBODIMENTS

[0013] In the present invention, a holding member that holds a leading end
of a through wiring is formed on a first surface side of a substrate
having the through wiring. Hence, when a thin film CMUT is manufactured
on the substrate having the through wiring, film damage due to a
difference in thermal expansion coefficient between the through wiring
and the substrate can be reduced.

[0014] Preferred embodiments of the present invention will now be
described in detail in accordance with the accompanying drawings.

First Embodiment

[0015] With reference to FIG. 1A and FIG. 1B, a basic configuration of a
first embodiment of a capacitive transducer of the present invention is
described. FIG. 1A is a cross-sectional view of the capacitive
transducer, and FIG. 1B is a plan view illustrating example shapes of a
holding member and a leading end of a through wiring and an example
positional relation therebetween. For the sake of simplicity, only one
cell (one vibration film) of the capacitive transducer is illustrated in
FIG. 1A.

[0016] As illustrated in FIG. 1A, the capacitive transducer of the present
embodiment includes: a substrate 1 having a first surface 1a and a second
surface 1b; and through wirings 2 (including 2-1 and 2-2) that pass
through the substrate 1 between the first surface 1a and the second
surface 1b that is opposed to each other. Moreover, the capacitive
transducer of the present embodiment has a cell structure in which a
vibration film 9 that can be vibrate is supported, the vibration film 9
including: a second electrode 6 that is provided with a gap 5 from a
first electrode 4 formed on the first surface side of the substrate 1;
and insulating films 7 and 8 that are respectively formed on lower and
upper sides of the second electrode 6. Then, a holding member 3 that
holds a leading end of each through wiring 2 is formed on the first
surface 1a side of the substrate 1. The substrate 1 is selected so as to
suit the performance of the capacitive transducer. For example, the
substrate 1 is made of an insulating material such as glass.
Alternatively, the substrate 1 may be made of any of high-resistance
silicon and low-resistance silicon. The thickness of the substrate 1 is,
for example, 100 μm to 1,000 μm.

[0017] Each through wiring 2 is made of a low-resistivity material. For
example, the through wiring 2 is made of a material containing metal.
Desirably, the through wiring 2 has a low-resistance structure containing
Cu as a main material thereof. The cross-sectional shape of the through
wiring 2 observed in a direction perpendicular to the first surface 1a of
the substrate 1 is designed in consideration of the capacitance and the
resistance of the through wiring 2 and the easiness in manufacturing the
through wiring 2. The cross-sectional shape of the through wiring 2 may
be uniform or non-uniform in the length direction thereof. As an example,
the cross-sectional shape of the through wiring 2 is substantially
circular, and the diameter thereof is 20 μm to 100 μm.

[0018] The holding member 3 for each through wiring 2 is formed on the
first surface 1a side of the substrate 1 so as to hold the leading end of
the through wiring 2. The holding member 3 has: a portion that closely
adheres to the first surface 1a of the substrate 1; a portion for holding
part of the leading end of the through wiring 2; and an opening for
exposing part of the leading end of the through wiring 2. The holding
member 3 is designed to have both features of the function of holding the
leading end of the through wiring 2 and the opening for enabling
connection between the through wiring 2 and one of the first electrode 4
and the second electrode 6. In particular, the holding member 3 is
designed such that deformation of the first electrode 4 and the vibration
film 9 due to maximum thermal deformation of the leading end of the
through wiring 2 on the first surface 1a side of the substrate 1 does not
influence the performance of the capacitive transducer. It is desirable
that the holding member 3 be made of a material having a high Young's
modulus. The holding member 3 may be a single-layer film or a multi-layer
film.

[0019] The strength of the holding member 3 is determined depending on the
material, the shape and the thickness thereof. For example, the holding
member 3 is designed such that the yield stress thereof in the length
direction of the through wiring 2 is equal to or more than 1.7 times the
shear strength of the through wiring 2. Under this condition, when the
through wiring 2 thermally deforms, the through wiring 2 starts to slide
in a direction opposite to the holding member 3 before significantly
deforming the holding member 3. As a result, even if the through wiring 2
deforms relative to the substrate 1 due to a difference in thermal
expansion coefficient between the substrate 1 and the through wiring 2 at
high temperature, the maximum stress that is applied by the through
wiring 2 to thin films on the upper surface of the holding member 3 is
suppressed. Accordingly, the thin films on the upper surface of the
holding member 3 can be prevented from significantly deforming and
breaking. In consideration of thermal deformation of the holding member 3
itself, it is desirable that the holding member 3 have a thermal
expansion coefficient closer to the thermal expansion coefficient of the
substrate 1 than the thermal expansion coefficient of the through wiring
2. For examples, the material of the holding member 3 may be any of
silicon compounds such as silicon oxide and silicon nitride, titanium
oxide (for example, TiO2), yttrium oxide (for example,
Y2O2) and aluminum oxide (for example, Al2O2). The
thickness of the holding member 3 is, for example, 0.1 μm to 2 μm.

[0020] FIG. 1B illustrates example shapes of the holding member and the
leading end of the through wiring and an example positional relation
therebetween. In FIG. 1B, the holding member 3 is a circular plate with
an opening having an inner circumference 3a and an outer circumference
3b, and is substantially concentric with the leading end of the through
wiring 2 having a circular outer circumference 2b. In the region between
the outer circumference 3b and the outer circumference 2b, the holding
member 3 closely adheres to the first surface 1a of the substrate 1. In
the region between the outer circumference 2b and the inner circumference
3a, the holding member 3 holds part of the leading end of the through
wiring 2. In the region on the inner side of the inner circumference 3a,
the holding member 3 has the opening, and a part 2a of the leading end of
the through wiring 2 is exposed. As a more specific example, the inner
circumference 3a of the holding member 3 is a circle having a diameter of
10 μm to 50 μm, and the distance between the inner circumference 3a
of the holding member 3 and the outer circumference 2b of the leading end
of the through wiring 2 is 5 μm to 50 μm. Moreover, the distance
between the outer circumference 3b of the holding member 3 and the outer
circumference 2b of the leading end of the through wiring 2 is 5 μm to
500 μm.

[0021] The holding member 3 may be rotationally symmetric or may not be
rotationally symmetric. Moreover, the holding member 3 may not be placed
concentrically with the leading end of the through wiring 2. Moreover,
the holding member 3 may be formed in direct contact with the first
surface 1a of the substrate 1, or may be formed on the first surface 1a
side of the substrate 1 with the intermediation of a film that closely
adheres to the first surface 1a of the substrate 1.

[0022] The first electrode 4 is formed on the first surface 1a side of the
substrate 1. In the case where the substrate 1 has insulation properties,
the first electrode 4 may be formed directly on the surface of the
substrate 1. Moreover, for the purpose of improving close adhesiveness
and electrical insulation properties, the first electrode 4 may be formed
on the first surface 1a side of the substrate 1 with the intermediation
of a film that closely adheres to the first surface 1a of the substrate
1. The first electrode 4 is connected to the through wiring 2-1 that is
one of the through wirings 2, and is further connected to an electrode
pad 11 formed on the second surface 1b side of the substrate 1 through
the through wiring 2-1.

[0023] The second electrode 6 is provided on the first surface 1a side of
the substrate 1 with the gap 5. For electrical insulation, the second
electrode 6 is formed so as to be sandwiched between the insulating films
7 and 8. The second electrode 6 is connected to the through wiring 2-2
that is one of the through wirings 2 by a wiring electrode 10, and is
further connected to an electrode pad 12 formed on the second surface 1b
side of the substrate 1 through the through wiring 2-2. The wiring
electrode 10 has a portion connected to the leading end of the through
wiring 2-2, and at least part of the outer circumference of the connected
portion is located on the inner side of the opening of the holding member
3. More desirably, the connected portion is located completely on the
inner side of the opening of the holding member 3. With this
configuration, even if film deformation occurs near the opening of the
holding member 3, the second electrode 6 and the leading end of the
through wiring 2-2 are reliably electrically connected to each other
regardless of the deformation. Both of the first electrode 4 and the
second electrode 6 may not be electrically drawn out to the second
surface 1b side of the substrate 1 through the through wirings 2, and
only any one thereof may be drawn out to the second surface 1b side
therethrough.

[0024] The area and the height (thickness) of the gap 5 are designed
depending on the performance of the capacitive transducer. When the
capacitive transducer is driven, the gap 5 deforms while following
vibrations of the vibration film 9. As an example, the gap 5 has a
structure close to a column having a diameter of 10 μm to 100 μm
and a height of 50 nm to 500 nm.

[0025] The insulating films 7 and 8 not only serve as insulating
protective films for the second electrode 6 but also form the vibration
film 9 of the cell together with the second electrode 6. The material and
the film thickness of each of the insulating films 7 and 8 are designed
depending on required performance and specifications of the capacitive
transducer. As an example, the insulating films 7 and 8 are made of
silicon nitride, and each have a thickness of 100 μm to 1,000 μm.
As a matter of course, the insulating films 7 and 8 may be made of
materials different from each other. Moreover, the insulating films 7 and
8 may be single-layer films or multi-layer films.

[0026] It is desirable that the vibration film 9 including the insulating
film 7, the second electrode 6 and the insulating film 8 have a tensile
stress of 1 GPa or less. In the case where the vibration film 9 has a
compressive stress, one of sticking and buckling may occur in the
vibration film 9, so that the vibration film 9 may significantly deform.
The sticking in this case means that the vibration film 9 sticks to the
first electrode 4 on the substrate 1 side. On the other hand, in the case
where the vibration film 9 has an excessively high tensile stress, the
vibration film 9 is likely to break. The material, the film thickness,
film formation conditions and heat treatment conditions of each of the
insulating film 7, the second electrode 6 and the insulating film 8 are
designed such that the vibration film 9 has a tensile stress of 1 GPa or
less. Moreover, for the purpose of improving close adhesiveness between
films and insulation properties and preventing interdiffusion, films
having such effects and functions may be respectively provided between
adjacent films of the insulating film 7, the second electrode 6, the
insulating film 8 and the wiring electrode 10.

[0027] Although not illustrated, the capacitive transducer is electrically
connected to a control circuit with the intermediation of the electrode
pads 11 and 12. Example methods used for this connection include
connection using bumps, wire bonding, and connection using an anisotropic
conductive film (ACF). When the capacitive transducer is driven, bias
voltage is applied to the first electrode 4, and the second electrode 6
is used as one of a signal application electrode and a signal take-out
electrode. Alternatively, the opposite may be adopted.

[0028] As described above, in the capacitive transducer of the present
embodiment, the leading end of each through wiring is held by the holding
member, on the substrate surface side on which the vibration film is
formed. Accordingly, even in a temperature rising state during
manufacture, the end part of the through wiring is suppressed from
protruding toward the holding member. As a result, even if the thermal
expansion coefficient of the through wiring and that of the substrate are
different from each other, damage of the vibration film and the lower
electrode of the capacitive transducer due to thermal deformation of the
through wiring can be prevented. Accordingly, the through wiring can be
made of a metal material different from the substrate material, and the
resistance of the through wiring can be remarkably reduced. Moreover, the
electrode and the through wiring can be reliably connected to each other.
In this way, the through wiring can be made of a low-resistivity metal
material, whereby the resistance of the through wiring can be remarkably
reduced. If the through wiring is made of such a low-resistivity metal
material, even if the through wiring is thinned, a sufficiently low
wiring resistance can be obtained. If the through wiring is thinned, a
substrate area occupied by the through wiring can be made smaller, and
the size of the capacitive transducer can be reduced.

Second Embodiment

[0029] A second embodiment related to a method of manufacturing a
capacitive transducer of the present invention is described. FIG. 2A to
FIG. 2Q are cross-sectional views for describing the manufacturing method
of the present embodiment. For the sake of simplicity, only one cell (one
vibration film) of the capacitive transducer is illustrated in FIG. 2A to
FIG. 2Q.

[0030] First, as illustrated in FIG. 2A, the substrate 1 having the first
surface 1a and the second surface 1b opposed to each other is prepared.
The substrate 1 is selected so as to suit the performance of the
capacitive transducer. For example, the substrate 1 is made of an
insulating material such as glass. Alternatively, the substrate 1 may be
made of any of high-resistance silicon and low-resistance silicon. In the
present embodiment, the substrate 1 made of low-resistance silicon is
taken as an example. The thickness of the substrate 1 is, for example,
100 μm to 1,000 μm. In order to reduce variation in performance
among cells, it is desirable that the first surface 1a of the substrate 1
be flat and smooth. For example, a surface roughness Ra of the first
surface 1a of the substrate 1 is less than 10 nm.

[0031] Then, as illustrated in FIG. 2B, through holes 13 are formed
penetrating the substrate 1 from the first surface 1a to the second
surface 1b, and the first surface 1a and the second surface 1b are
opposed to each other. Each through hole 13 functions as a hole for
inserting a predetermined through electrode (through wiring) 2. The
cross-sectional shape of the through hole 13 may be uniform or
non-uniform in the length direction thereof. As an example, the through
hole 13 has a substantially columnar shape having a diameter of 20 μm
to 100 μm. The through hole 13 is formed using, for example, a deep
reactive ion etching (RIE) technique of silicon. The substrate 1 is
processed using RIE from both sides of the first surface 1a and the
second surface 1b if needed. Moreover, if needed, an inner wall 13a of
the through hole 13 is smoothed such that a surface roughness Rmax of the
inner wall 13a becomes less than 100 nm.

[0032] Then, as illustrated in FIG. 2C, an insulating film 14 is formed on
the surface of the substrate 1 including the first surface 1a, the second
surface 1b and the inner wall 13a of each through hole 13 (see FIG. 2B).
The insulating film 14 is made of, for example, any of silicon oxide,
silicon nitride and aluminum oxide (Al2O3), and a material
having high insulation properties is desirably used therefor. The
thickness of the insulating film 14 is determined by required dielectric
strength voltage and material characteristics. The thickness of the
insulating film 14 is, for example, 0.1 μm to 2 μm. For example,
the methods of forming the insulating film 14 include thermal oxidation,
chemical vapor deposition (CVD), and atomic layer deposition (ALD). The
insulating film 14 may be a single-layer film or a multi-layer film.
Moreover, if needed, a close adhesion layer may be formed between the
surface of the substrate 1 and the insulating film 14.

[0033] Then, as illustrated in FIG. 2D, an insulating film 15 is further
formed on the surface of the insulating film 14. One of roles of the
insulating film 15 having insulation properties is to serve as a barrier
layer for preventing the material of the through wirings 2 to be formed
in FIG. 2E from diffusing to the insulating film 14. The insulating film
15 is made of, for example, any of silicon nitride and titanium nitride.
The thickness of the insulating film 15 is, for example, 0.01 μm to
0.5 μm. The insulating film 15 is formed using, for example, the CVD
method.

[0034] Then, as illustrated in FIG. 2E, the through wirings 2 that
penetrate the substrate 1 from the first surface 1a to the second surface
1b, the first surface 1a and he second surface 1b are opposed to each
other, are respectively formed in the through holes 13 (see FIG. 2B).
Each through wiring 2 is made of a low-resistivity material. Desirably,
the through wiring 2 is made of a material containing metal. For example,
the through wiring 2 has a structure containing Cu as a main material
thereof. The through wiring 2 is formed so as to substantially fill the
inside of the through hole 13. Example methods of forming the through
wiring 2 include plating. In particular, a method in which electrolytic
plating is performed with one surface of the substrate 1 (for example,
the second surface 1b of the substrate 1) closely adhering to a substrate
with a seed layer can be adopted. After the plating, the substrate with
the seed layer is separated from the substrate 1. Then, the first surface
1a and the second surface 1b of the substrate 1 are planarized by
polishing. Chemical mechanical polish (CMP) is preferable as the
polishing method. The surface roughness Ra of the first surface 1a of the
substrate 1 is made less than 10 nm by performing CMP. For example, in
the case where the through wiring 2 contains Cu as the main material
thereof, after the plating, the end surfaces of the through wiring 2 and
the surfaces 1a and 1b of the substrate 1 are polished into substantially
the same height (level) by performing CMP of Cu. In this case, the
insulating film 15 (made of, for example, silicon nitride) serves as a
stopper layer for the CMP of Cu. Then, if needed, the surface roughness
of the first surface 1a of the substrate 1 is reduced by performing CMP
on the insulating film 15.

[0035] In FIG. 2E, seemingly, two through wirings 2 are formed for one
vibration film (one cell). In actual use, two through wirings 2 may be
formed for a plurality of vibration films. For example, two through
wirings 2 are formed for one element including a plurality of vibration
films. The number of the through holes 13 corresponds to the number of
the through wirings 2.

[0036] Then, as illustrated in FIG. 2F, the holding member 3 that holds
the leading end of each through wiring 2 is formed on the first surface
1a side of the substrate 1. The holding member 3 includes: the portion
that closely adheres to the first surface 1a of the substrate 1; the
portion for holding part of the leading end of the through wiring 2; and
the opening for exposing the part 2a of the leading end of the through
wiring 2. The holding member 3 is designed such that deformation of the
first electrode 4 and the vibration film 9 due to maximum thermal
deformation of the leading end of the through wiring 2 in the subsequent
heat treatment does not influence the performance of the cell. It is
desirable that the holding member 3 be made of a material having a high
Young's modulus. The holding member 3 may be a single-layer film or a
multi-layer film. The strength of the holding member 3 is determined
depending on the material, the shape and the thickness thereof. For
example, the holding member 3 is formed such that the yield stress
thereof in the length direction of the through wiring 2 is equal to or
more than 1.7 times the shear strength of the through wiring 2. Moreover,
in consideration of thermal deformation of the holding member 3, it is
desirable that the holding member 3 have a thermal expansion coefficient
closer to the thermal expansion coefficient of the substrate 1 than the
thermal expansion coefficient of the through wiring 2.

[0037] For examples, the material of the holding member 3 include silicon
oxide, silicon nitride, titanium oxide (for example, TiO2), yttrium
oxide (for example, Y2O3) and aluminum oxide (for example,
Al2O3). The thickness of the holding member 3 is, for example,
0.1 μm to μm. The shape of the holding member 3 is, for example, a
circular plate substantially concentric with the through wiring 2, as
illustrated in FIG. 1B. The form of the holding member 3 is, for example,
as described in the first embodiment. It is desirable that, when the
holding member 3 is formed, relative deformation between the leading end
of the through wiring 2 and the first surface 1a of the substrate 1 be as
small as possible. Accordingly, it is desirable that the holding member 3
be formed at a temperature of 100° C. or lower. It is more
desirable that the holding member 3 be formed at a temperature close to
room temperature. A method of forming a film of the holding member 3 may
be sputtering method. As a method of forming a pattern of the holding
member 3, etching mask formation including photolithography, dry etching
including reactive ion etching, or wet etching using chemicals can be
used.

[0038] Then, as illustrated in FIG. 2G, the first electrode 4 is formed on
the first surface 1a side of the substrate 1. The first electrode 4 is
one of electrodes for driving the vibration film. The first electrode 4
is formed on the insulating film 14 and the insulating film 15, and hence
being insulated from the substrate 1. The first electrode 4 includes: a
portion located below a vibrating portion (a portion corresponding to the
gap 5 in FIG. 20) of the vibration film 9 of the cell; and a portion 4a
connected to the through wiring 2-1 that is one of the through wirings 2.
The first electrode 4 is made of a material having high electrical
conductivity. For example, the first electrode 4 is made of a film
containing metal as a main component thereof. As an example, the first
electrode 4 is made of a film containing Al as a main component thereof.
The first electrode 4 may be comprised of a single-layer film or a
multi-layer film. The first electrode 4 is electrically conductively
formed for each cell in the same element. For example, as a method of
forming the first electrode 4, a method including formation of a metal
film, photolithography, dry etching and wet etching of the metal film can
be used. The metal film is formed so as not to be disconnected around the
holding member 3. A film forming method that gives excellent coating
property, such as sputtering, is desirable to form the metal film.

[0039] Then, as illustrated in FIG. 2H, an insulating film 16 is formed.
The insulating film 16 covers the surface of the first electrode 4, and
one of roles thereof is to serve as an insulating protective film for the
first electrode 4. The insulating film 16 is made of, for example, any of
silicon oxide, silicon nitride and aluminum oxide (Al2O3) , and
they desirably have high insulation properties. The thickness of the
insulating film 16 is determined by required dielectric strength voltage
and material characteristics, and for example, the thickness is 0.1 μm
to 2 μm. It is desirable that the insulating film 16 be formed at a
temperature of 400° C. or lower. For example, as a method of
forming the insulating film 16, chemical vapor deposition, atomic layer
deposition and sputtering can be used. The insulating film 16 may be a
single-layer film or a multi-layer film. Moreover, if needed, a close
adhesion layer may be formed under the insulating film 16.

[0040] Then, as illustrated in FIG. 2I, a sacrifice layer 17 is formed.
The sacrifice layer 17 serves to define the gap 5 (see FIG. 2N) of the
cell, and is made of a material that can be selectively removed when the
gap 5 is formed. The sacrifice layer 17 is made of, for example, one of a
silicon-based material or metal such as Cr. As a method of forming a
pattern of the sacrifice layer 17, a method including etching mask
formation including photolithography, and dry etching including reactive
ion etching or wet etching using chemicals can be used.

[0041] Then, as illustrated in FIG. 2J, a hole 16a is formed. The hole 16a
is an opening of the insulating film 16, and serves to connect the second
electrode 6 to the through wiring 2-2 that is one of the through wirings
2 (see FIG. 2Q). The hole 16a can preferably be slightly larger than the
opening 3a of the holding member 3. As a method of forming the hole 16a,
a method including etching mask formation including photolithography, and
dry etching including reactive ion etching or wet etching using chemicals
can be used.

[0042] Then, as illustrated in FIG. 2K, the insulating film 7 is formed.
The insulating film 7 spreads in contact with the entire lower surface of
the second electrode 6 to be formed in FIG. 2L, and one of roles thereof
is to serve as an insulating protective film for the second electrode 6.
The insulating film 7 is made of, for example, any of silicon oxide,
silicon nitride and aluminum oxide (Al2O3), and they desirably
have high insulation properties. The thickness of the insulating film 7
is determined by required dielectric strength voltage and material
characteristics, and for example, the thickness is 0.1 μm to 2 μm.
It is desirable that the insulating film 7 be formed at a temperature of
400° C. or lower. For example, as a method of forming the
insulating film 7, chemical vapor deposition, atomic layer deposition and
sputtering can be used. The insulating film 7 may be a single-layer film
or a multi-layer film.

[0043] Then, as illustrated in FIG. 2L, the second electrode 6 is formed.
The second electrode 6 is formed as part of the vibration film 9 so as to
be opposed to the first electrode 4, and the second electrode 6 is one of
electrodes for driving the vibration film 9 (see FIG. 20). The second
electrode 6 may have a configuration similar to the configuration of the
first electrode 4, and may be formed in a manner similar to the manner of
the first electrode 4. Moreover, the second electrode 6 is electrically
conductively formed for each cell in the same element.

[0044] Then, as illustrated in FIG. 2M, the insulating film 8 is formed.
The insulating film 8 spreads in contact with the entire upper surface of
the second electrode 6, and one of roles thereof is to serve as an
insulating protective film for the second electrode 6. It is desirable
that the insulating film 8 be formed at a temperature of 400° C.
or lower. The insulating film 8 may have a configuration similar to the
configuration of the insulating film 7, and may be formed in a manner
similar to the manner of the insulating film 7.

[0045] Then, as illustrated in FIG. 2N, an etching hole 18 is formed, and
the sacrifice layer 17 (see FIG. 2M) is removed. The etching hole 18 is
an opening that passes through the insulating films 7 and 8 and serves to
etch the sacrifice layer 17. As a method of forming the etching hole 18,
a method including etching mask formation including photolithography, and
dry etching including reactive ion etching or wet etching using chemicals
can be used. The sacrifice layer 17 is removed using etching liquid or
etching gas through the etching hole 18. As a result of the removal of
the sacrifice layer 17, the gap 5 is formed.

[0046] Then, as illustrated in FIG. 2O, a thin film 19 is formed. The thin
film 19 seals the etching hole 18, and forms the vibration film 9 that
can vibrate above the gap 5, together with the insulating film 7, the
second electrode 6 and the insulating film 8. The material and the
thickness etc. of the thin film 19 are determined so as to favorably seal
the etching hole 18 and suit the performance of the vibration film 9. It
is desirable that the thin film 19 be formed at a temperature of
400° C. or lower. The thin film 19, which is an insulating film,
may have a configuration similar to the configuration of the insulating
film 7, and the thin film 19 may be formed in a manner similar to the
manner of the insulating film 7. If needed, the thickness of the thin
film 19 is made smaller within a range which the sealing of the etching
hole 18 is not influenced, whereby the mechanical performance of the
vibration film 9 is adjusted.

[0047] It is desirable that the vibration film 9 including the insulating
film 7, the second electrode 6, the insulating film 8 and the thin film
19 have a tensile stress of 1 GPa or less. In the case where the
vibration film 9 has a compressive stress, one of sticking and buckling
may occur in the vibration film 9, so that the vibration film 9 may
significantly deform. The sticking, in this case, means that the
vibration film 9 as a structure sticks to the insulating film 16 on the
substrate side after the removal of the sacrifice layer 17. On the other
hand, in the case where the vibration film 9 has a high tensile stress,
the vibration film 9 is likely to break. The material, the film
thickness, film formation conditions and heat treatment conditions after
the film formation of each of the insulating film 7, the second electrode
6, the insulating film 8 and the thin film 19 are designed such that the
vibration film 9 has a tensile stress of 1 GPa or less.

[0048] Then, as illustrated in FIG. 2P, contact holes 20 (including 20a
and 20b) are formed on the first surface 1a side of the substrate 1 (see
FIG. 2A), and a contact hole 21 is formed on the second surface 1b side
of the substrate 1 (see FIG. 2A). At least part of the outer
circumference of the contact hole 20a is located on the inner side of the
opening of the holding member 3. More desirably, the contact hole 20a is
completely located on the inner side of the opening of the holding member
3. As a method of forming the contact holes 20 and 21, a method including
etching mask formation including photolithography, and dry etching
including reactive ion etching or wet etching using chemicals can be
used.

[0049] Then, as illustrated in FIG. 2Q, the connection wiring 10 is formed
on the first surface 1a side of the substrate 1, and the electrode pads
11, 12 and 22 are formed on the second surface 1b side of the substrate
1. The connection wiring 10 connects the second electrode 6 to the
through wiring 2-2 (see FIG. 2F) through the contact holes 20a and 20b
(see FIG. 2P). The electrode pad 11 connected to the through wiring 2-1
(see FIG. 2F) and the electrode pad 12 connected to the through wiring
2-2 (see FIG. 2F) are formed on the second surface 1b side of the
substrate 1. Moreover, the electrode pad 22 that is connected to the
substrate 1 through the contact hole 21 (see FIG. 2P) is formed on the
second surface 1b side of the substrate 1. Because at least part of the
outer circumference of the contact hole 20a is located on the inner side
of the opening of the holding member 3, even if film deformation occurs
near the opening of the holding member 3, the second electrode 6 and the
leading end of the through wiring 2-2 can be reliably connected to each
other. The methods of forming the connection wiring 10 and the electrode
pads 11, 12 and 22 may be, for example, similar to the method of forming
the first electrode 4.

[0050] In the present embodiment, as illustrated in FIG. 2G, the first
electrode 4 and the through wiring 2-1 are connected to each other by
forming the portion 4a of the first electrode 4 directly on the leading
end of the through wiring 2-1. Alternatively, the first electrode 4 and
the through wiring 2-1 can also be connected to each other similarly to
the connection between the second electrode 6 and the through wiring 2-2
using the contact holes 20 and the connection wiring 10.

[0051] For the purpose of improving close adhesiveness between films,
insulation properties, and preventing interdiffusion, the above-mentioned
manufacturing method includes respectively providing films having such
effects and functions between adjacent films. Moreover, for the purpose
of improving close adhesiveness between films, it is effective to apply
surface treatment on each underlying film before forming a next film
thereon. The surface of the underlying film is cleaned or activated by
the surface treatment. For examples, as a surface treatment, plasma
treatment or treatment using liquid can be used.

[0052] Then, although not illustrated, the capacitive transducer is
connected to the control circuit with the intermediation of the electrode
pads 11, 12 and 22. As a method for this connection, direct connection of
metal parts, connection using bumps, connection using an ACF and wire
bonding can be used. When the capacitive transducer is driven, bias
voltage is applied to the first electrode 4, and the second electrode 6
is used as a signal application electrode or a signal take-out electrode.
Alternatively, the opposite may be adopted. In needed, the substrate 1 is
grounded through the electrode pad 22 to reduce signal noise.

[0053] As described above, according to the method of manufacturing the
capacitive transducer of the present embodiment, the leading end of each
through wiring is held by the holding member on the substrate surface on
which the vibration film is formed. Accordingly, such effects as
described in the first embodiment can be produced.

[0054] Hereinafter, more specific examples are described.

EXAMPLE 1

[0055] With reference to FIG. 1A and FIG. 1B, a basic configuration
example of a capacitive transducer of Example 1 is described. The
capacitive transducer of the present example has such a configuration as
illustrated in FIG. 1A.

[0056] The substrate 1 is made of insulating glass having both surfaces
that are mirror-polished, and the surface roughness Ra thereof is less
than 5 nm. The thickness of the substrate 1 is 180 μm. Each through
wiring 2 has a columnar structure containing Cu as a main material
thereof. The leading ends of the through wiring 2 are respectively
exposed on the first surface 1a and the second surface 1b of the
substrate 1, and the diameter of the outer circumference 2b of the
leading ends are about 30 μm.

[0057] The holding member 3 is formed so as to hold the leading end of the
through wiring 2 on the first surface 1a side of the substrate 1. As
illustrated in FIG. 1A and FIG. 1B, the holding member 3 has a circular
plate shape, the diameter of the inner circumference 3a is about 20
μm, the diameter of the outer circumference 3b is about 50 μm, and
the holding member 3 is substantially concentric with the leading end of
the through wiring 2. In the region between the outer circumference 3b
and the outer circumference 2b, the holding member 3 closely adheres to
the first surface 1a of the substrate 1. In the region between the outer
circumference 2b and the inner circumference 3a, the holding member 3
holds part of the leading end of the through wiring 2. In the region on
the inner side of the inner circumference 3a, the holding member 3 has
the opening having a diameter of about 20 μm, and the part 2a of the
leading end of the through wiring 2 is exposed.

[0058] The first electrode 4 is formed on the first surface 1a side of the
substrate 1, and covers an entire region below the gap 5. Moreover, the
first electrode 4 is connected to the through wiring 2-1 that is one of
the through wirings 2, and the first electrode 4 is further connected to
the electrode pad 11 formed on the second surface 1b side of the
substrate 1 through the through wiring 2-1. The first electrode 4 is
formed by laminating a Ti film having a thickness of 5 nm and an aluminum
alloy (an alloy obtained by mixing small amounts of Si and Cu with Al as
a main component) film having a thickness of 200 nm in order on the first
surface 1a of the substrate 1. A main role of the Ti film is to improve
close adhesiveness of the first electrode 4 to the first surface 1a of
the substrate 1.

[0059] The second electrode 6 is provided on the first surface 1a side of
the substrate 1 with the gap 5 from the first electrode 4. For electrical
insulation, the second electrode 6 is formed so as to be sandwiched
between the insulating films 7 and 8. The second electrode 6 is connected
to the through wiring 2-2 that is one of the through wirings 2 by the
wiring electrode 10, and the through wiring 2-2 is further connected to
the electrode pad 12 formed on the second surface 1b side of the
substrate 1 through the through wiring 2-2. The portion of the wiring
electrode 10 connected to the leading end of the through wiring 2-2 is
located completely on the inner side of the opening of the holding member
3, and reliably connects the second electrode 6 to the leading end of the
through wiring 2-2. The second electrode 6 is formed by laminating a Ti
film having a thickness of 5 nm, an aluminum alloy (an alloy obtained by
mixing small amounts of Si and Cu with Al as a main component) film
having a thickness of 200 nm and a Ti film of 5 nm in order. A main role
of the Ti film is to: improve close adhesiveness of the second electrode
6 to the insulating films 7 and 8; and prevent interdiffusion.

[0060] The gap 5 has a columnar structure having a diameter of about 30
μm and a height of 150 nm. The insulating films 7 and 8 function as
insulating protective films for the second electrode 6, and they form the
vibration film 9 of the cell together with the second electrode 6. The
insulating films 7 and 8 are each made of silicon nitride. The thickness
of the insulating film 7 is 200 μm, and the thickness of the
insulating film 8 is 400 μm. The vibration film 9 including the
insulating film 7, the second electrode 6 and the insulating film 8 has a
tensile stress of 0.7 GPa or less. This is achieved by adjusting film
formation conditions of the insulating film 7, the second electrode 6 and
the insulating film 8 and heat treatment conditions after the film
formation.

[0061] The wiring electrode 10 is formed by laminating a Ti film having a
thickness of 5 nm and an aluminum alloy (an alloy obtained by mixing
small amounts of Si and Cu with Al as a main component) film having a
thickness of 200 nm in order. A main role of the Ti film is to: improve
close adhesiveness of the wiring electrode 10 to the insulating films 7
and 8; and prevent interdiffusion. The electrode pads 11 and 12 are each
formed by laminating a Cr film having a thickness of 5 nm and an Al film
having a thickness of 200 nm in order. A main role of the Cr film is to
provide the electrode pads 11 and 12 with favorable close adhesiveness to
the second surface 1b of the substrate 1 and the leading ends the through
wirings 2 (including 2-1 and 2-2).

[0062] Although not illustrated, the capacitive transducer is connected to
the control circuit using an ACF with the intermediation of the electrode
pads 11 and 12. When the capacitive transducer is driven, bias voltage is
applied to the first electrode 4, and the second electrode 6 is used as a
signal application electrode or a signal take-out electrode.

[0063] Also in the present example, such effects as described in the first
embodiment can be produced.

EXAMPLE 2

[0064] With reference to FIG. 2A to FIG. 2Q, an example method of
manufacturing a capacitive transducer of Example is described. First, as
illustrated in FIG. 2A, the substrate 1 having the first surface 1a and
the second surface 1b is prepared. The substrate 1 is made of
low-resistance silicon having both surfaces that are mirror-polished,
surface roughness Ra thereof is less than 2 nm, and the resistivity
thereof is 0.01 Ωcm. The thickness of the substrate 1 is 200 μm.

[0065] Then, as illustrated in FIG. 2B, the through holes 13 are formed
penetrating the substrate 1 from the first surface 1a to the second
surface 1b are formed. Each through hole 13 has a substantially columnar
shape, and the diameter of the opening thereof on each of the first
surface 1a and the second surface 1b of the substrate 1 is about 20
μm. The through hole 13 is formed using the deep RIE technique of
silicon. After the deep RIE, the inner wall 13a of the through hole 13 is
smoothed by repeating thermal oxidation of the silicon and removal of the
resultant thermally oxidized film several times. Then, as illustrated in
FIG. 2C, the insulating film 14 is formed on the surface of the substrate
1 including the first surface 1a, the second surface 1b and the inner
wall 13a of each through hole 13 (see FIG. 2B). The insulating film 14 is
made of silicon oxide having a thickness of about 1 μm, and is formed
by thermal oxidation of silicon.

[0066] Then, as illustrated in FIG. 2D, the insulating film 15 is further
formed on the surface of the insulating film 14. One of roles of the
insulating film 15 is to serve as a barrier layer for preventing the
material of the through wirings 2 to be formed in FIG. 2E from diffusing
to the insulating film 14. The insulating film 15 is made of silicon
nitride having a thickness of about 100 nm, and is formed using low
pressure CVD (LP-CVD).

[0067] Then, as illustrated in FIG. 2E, the through wirings 2 that
penetrate the substrate 1 from the first surface 1a to the second surface
1b are respectively formed in the through holes 13. Each through wiring 2
contains Cu as a main material thereof, and substantially fills the
inside of the through hole 13. The through wiring 2 is formed using
electrolytic plating and a polishing technique. Specifically, first,
electrolytic plating of Cu is performed with the second surface 1b of the
substrate 1 closely adhering to a substrate with a seed layer (not
illustrated). After the plating, the substrate with the seed layer is
removed. Then, CMP is performed on the first surface 1a and the second
surface 1b of the substrate 1, whereby the first surface 1a and the
second surface 1b are planarized. When the CMP is performed on Cu, the
insulating film 15 made of silicon nitride serves as a stopper layer for
the CMP on Cu. After the CMP on Cu, CMP is performed on the insulating
film 15. After the CMP, the surface roughness Ra of the first surface 1a
of the substrate 1 becomes less than 5 nm. Moreover, the leading ends of
the through wiring 2 are respectively concaved by about 0.5 μm at the
maximum with respect to the first surface 1a and the second surface 1b of
the substrate 1.

[0068] Then, as illustrated in FIG. 2F, the holding member 3 that holds
the leading end of each through wiring 2 is formed on the first surface
1a side of the substrate 1. As illustrated in FIG. 2F and FIG. 1B, the
holding member 3 is a circular plate whose inner circumference 3a has a
diameter of about 12 μm and whose outer circumference 3b has a
diameter of about 30 μm, and is substantially concentric with the
leading end of the through wiring 2. In the region between the outer
circumference 3b and the outer circumference 2b, the holding member 3
closely adheres to the first surface 1a of the substrate 1 with the
intermediation of the insulating films 14 and 15. In the region between
the outer circumference 2b and the inner circumference 3a, the holding
member 3 holds part of the leading end of the through wiring 2. In the
region on the inner side of the inner circumference 3a, the part 2a
(having a diameter of about 12 μm) of the leading end of the through
wiring 2 is exposed. The holding member 3 is made of silicon oxide having
a thickness of about 1 μm. The film of the silicon oxide is formed
using sputtering at a substrate temperature of 50° C. or lower.
The pattern of the holding member 3 is formed using a method including
photolithography and reactive ion etching.

[0069] Then, as illustrated in FIG. 2G, the first electrode 4 is formed on
the first surface 1a side of the substrate 1. The first electrode 4 is
one of electrodes for driving the vibration film. The first electrode 4
covers the entire region below the gap 5, and includes: the portion
located below the vibrating portion of the vibration film 9; and the
portion 4a connected to the through wiring 2-1 that is one of the through
wirings 2. The first electrode 4 is electrically conductively formed for
each cell in the same element. The first electrode 4 is formed by
laminating a Ti film having a thickness of 5 nm and an aluminum alloy
film having a thickness of 200 nm in order. A main role of the Ti film is
to secure close adhesiveness of the first electrode 4 to an underlying
film. The first electrode 4 is formed using a method including formation
of a metal film by sputtering, photolithography and dry etching of the
metal film.

[0070] Then, as illustrated in FIG. 2H, the insulating film 16 is formed.
The insulating film 16 covers the surface of the first electrode 4, and
one of roles thereof is to serve as an insulating protective film for the
first electrode 4. The insulating film 16 is a film of silicon oxide
having a thickness of 200 nm, and is formed using CVD at a substrate
temperature of about 300° C.

[0071] Then, as illustrated in FIG. 2I, the sacrifice layer 17 is formed.
The sacrifice layer 17 serves to define the gap 5 of the cell, and is
made of Cr. First, a Cr film is formed using electron beam evaporation.
Then, the Cr film is processed into a desired shape using a method
including photolithography and wet etching. The sacrifice layer 17 is
formed so as to have a columnar structure having a diameter of about 30
μm and a height of 150 nm.

[0072] Then, as illustrated in FIG. 2J, the hole 16a is formed. The hole
16a is an opening of the insulating film 16, and the opening serves to
connect the second electrode 6 to the through wiring 2-2 that is one of
the through wirings 2. The hole 16a has a circular shape having a
diameter of about 15 μm, and is substantially concentric with the
opening 3a of the holding member 3.

[0073] Then, as illustrated in FIG. 2K, the insulating film 7 is formed.
The insulating film 7 spreads in contact with the entire lower surface of
the second electrode 6 to be formed in FIG. 2L, and one of roles thereof
is to serve as an insulating protective film for the second electrode 6.
The insulating film 7 is made of silicon nitride having a thickness of
200 nm. The film of the silicon nitride is formed using plasma enhanced
CVD (PE-CVD) at a substrate temperature of about 300° C. During
the film formation, the flow rate of film formation gas is controlled
such that the film of the silicon nitride as the insulating film 7 has a
tensile stress of about 0.1 GPa.

[0074] Then, as illustrated in FIG. 2L, the second electrode 6 is formed.
The second electrode 6 is formed above the vibration film so as to be
opposed to the first electrode 4, and the second electrode 6 is one of
electrodes for driving the vibration film 9. The second electrode 6 has a
configuration similar to the configuration of the first electrode 4, and
is formed in a manner similar to the manner of the first electrode 4.
Moreover, the second electrode 6 is electrically conductively formed for
each cell in the same element. Film formation conditions of the second
electrode 6 are adjusted such that the second electrode 6 has a tensile
stress of 0.4 GPa or less when the manufacture of the capacitive
transducer is completed.

[0075] Then, as illustrated in FIG. 2M, the insulating film 8 is formed.
The insulating film 8 spreads in contact with the entire upper surface of
the second electrode 6, and one of roles thereof is to serve as an
insulating protective film for the second electrode 6. The insulating
film 8 has a configuration similar to the configuration of the insulating
film 7, and is formed in a manner similar to the manner of the insulating
film 7.

[0076] Then, as illustrated in FIG. 2N, the etching hole 18 is formed, and
the sacrifice layer 17 is removed. First, the etching hole 18 is formed
using a method including photolithography and reactive ion etching. Then,
the sacrifice layer 17 is removed by introducing etching liquid through
the etching hole 18. As a result, the gap 5 having the same shape as the
shape of the sacrifice layer 17 is formed.

[0077] Then, as illustrated in FIG. 2O, the thin film 19 is formed. The
thin film 19 seals the etching hole 18, and forms the vibration film 9
that can vibrate above the gap 5, together with the insulating film 7,
the second electrode 6 and the insulating film 8. The thin film 19 is
made of silicon nitride having a thickness of 300 nm. The thin film 19 is
formed using PE-CVD at a substrate temperature of about 300° C.,
similarly to the insulating film 7. The thin film 19 has a tensile stress
of about 0.1 GPa. The vibration film 9 formed in this way has a tensile
stress of about 0.7 GPa as a whole. Hence, sticking and buckling do not
occur in the vibration film 9, and the vibration film 9 is less likely to
break.

[0078] Then, as illustrated in FIG. 2P, the contact holes 20 (including
20a and 20b) are formed on the first surface 1a side of the substrate 1,
and the contact hole 21 is formed on the second surface 1b side of the
substrate 1. The contact hole 20a has a columnar shape having a diameter
of about 10 μm, and the outer circumference thereof is located on the
inner side of the opening 3a of the holding member 3. The contact holes
20 (including 20a and 20b) and the contact hole 21 are formed using a
method including photolithography and reactive ion etching.

[0079] Then, as illustrated in FIG. 2Q, the connection wiring 10 and the
electrode pads 11, 12 and 22 are formed respectively. The connection
wiring 10 is formed on the first surface 1a side of the substrate 1. The
connection wiring 10 connects the second electrode 6 to the through
wiring 2-2 that is one of the through wirings 2, through the contact
holes 20a and 20b. Because the outer circumference of the contact hole
20a is located on the inner side of the opening of the holding member 3,
even if film deformation occurs near the opening of the holding member 3,
the second electrode 6 and the leading end of the through wiring 2-2 are
reliably connected to each other by the connection wiring 10. The
electrode pad 11 connected to the through wiring 2-1 and the electrode
pad 12 connected to the through wiring 2-2 are formed on the second
surface 1b side of the substrate 1. Moreover, the electrode pad 22 that
is connected to the substrate 1 through the contact hole 21 is formed on
the second surface 1b side of the substrate 1. The connection wiring 10
and the electrode pads 11, 12 and 22 have the same configuration as the
configuration of the first electrode 4, and are formed in the same manner
as the manner of the first electrode 4.

[0080] For the purpose of improving close adhesiveness between the
insulating films 7, 8 and 19, the above-mentioned manufacturing method
includes applying plasma treatment on the surface of each underlying film
before forming a next film thereon. The surface of the underlying film is
cleaned or activated by the plasma treatment. Then, although not
illustrated, the capacitive transducer is connected to the control
circuit using an ACF with the intermediation of the electrode pads 11, 12
and 22. When the capacitive transducer is driven, bias voltage is applied
to the first electrode 4, and the second electrode 6 is used as one of a
signal application electrode or a signal take-out electrode. The
substrate 1 is grounded through the electrode pad 22 to reduce signal
noise.

[0081] As described above, according to the method of manufacturing the
capacitive transducer of the present example, the leading end of each
through wiring is held by the holding member on the substrate surface on
which the vibration film is formed. Accordingly, such effects as
described in the first embodiment can be produced.

EXAMPLE 3

[0082] FIG. 3A illustrates an example subject information acquiring
apparatus using a photoacoustic effect. Pulsed light emitted from a light
source 2010 passes through an optical member 2012 such as a lens, a
mirror and an optical fiber, and a subject 2014 is irradiated with the
pulsed light. A light absorber 2016 provided inside of the subject 2014
absorbs energy of the pulsed light, and generates photoacoustic waves
2018 that are acoustic waves. A capacitive transducer 2020 of the present
invention provided inside of a probe 2022 receives the photoacoustic
waves 2018, and the capacitive transducer 2020 converts the photoacoustic
waves 2018 into electric signals. Then the capacitive transducer 2020
outputs the electric signals to a signal processing unit 2024. The signal
processing unit 2024 performs signal processing such as A/D conversion
and amplification on the received electric signals, and outputs the
processed signals to a data processing unit 2026. The data processing
unit 2026 acquires subject information (characteristic information in
which optical characteristic values of the subject, such as a light
absorption coefficient, are reflected) as image data using the received
signals. Here, the signal processing unit 2024 and the data processing
unit 2026 are collectively referred to as processing unit. A display unit
2028 displays an image based on the image data received from the data
processing unit 2026. As described above, the subject information
acquiring apparatus of the present example includes: the capacitive
transducer of the present invention; the light source; and the data
processing unit. Then, the transducer receives the photoacoustic waves
generated by irradiating the subject with the light emitted from the
light source, and converts the received waves into the electric signals.
The data processing unit acquires the subject information using the
electric signals.

[0083] FIG. 3B illustrates an example subject information acquiring
apparatus such as an ultrasonographic diagnostic apparatus using
reflection of acoustic waves. A capacitive transducer 2120 of the present
invention provided inside of a probe 2122 transmits acoustic waves to a
subject 2114, and the acoustic waves are reflected on a reflector 2116.
The transducer 2120 receives the reflected acoustic waves (reflected
waves) 2118, and the capacitive transducer 2120 converts the reflected
waves 2118 into electric signals. Then the capacitive transducer 2120
outputs the electric signals to a signal processing unit 2124. The signal
processing unit 2124 performs signal processing such as A/D conversion
and amplification on the received electric signals, and outputs the
processed signals to a data processing unit 2126. The data processing
unit 2126 acquires subject information (characteristic information in
which a difference in acoustic impedance is reflected) as image data
using the received signals. Also in this example, the signal processing
unit 2124 and the data processing unit 2126 are collectively referred to
as processing unit. A display unit 2128 displays an image based on the
image data received from the data processing unit 2126. As described
above, the subject information acquiring apparatus of the present example
includes: the capacitive transducer of the present invention; and the
processing unit that acquires the subject information using the electric
signals received from the transducer. The transducer receives the
acoustic waves from the subject, and outputs the electric signals.

[0084] Note that the probe may be a probe that mechanically moved for
scanning or a probe that are moved by a user such as a doctor and an
operator with respect to the subject (handheld type). Moreover, in the
case of the apparatus using the reflected waves as illustrated in FIG.
3B, a probe for transmitting acoustic waves may be provided separately
from a probe for receiving acoustic waves. Further, both the functions of
the apparatuses of FIG. 3A and FIG. 3B may be provided to one apparatus,
and both the subject information in which optical characteristic values
of the subject are reflected and the subject information in which a
difference in acoustic impedance is reflected may be acquired. In this
case, the transducer 2020 of FIG. 3A may be capable of not only
performing the photoacoustic wave reception but also both the acoustic
wave transmission and the reflected wave reception.

[0085] In the capacitive transducer of the present invention, the leading
end of each through wiring is held by the holding member, on the
substrate surface side on which the vibration film is formed.
Accordingly, even in a temperature rising state during manufacture, the
end part of the through wiring is suppressed from protruding from the
substrate surface on the vibration film side.

[0086] While the present invention has been described with reference to
exemplary embodiments, it is to be understood that the invention is not
limited to the disclosed exemplary embodiments. The scope of the
following claims is to be accorded the broadest interpretation so as to
encompass all such modifications and equivalent structures and functions.

[0087] This application claims the benefit of Japanese Patent Application
No. 2013-273672, filed Dec. 28, 2013, which is hereby incorporated by
reference herein in its entirety.